As the demand for fuels such as aviation fuel increases worldwide there is increasing interest in feedstock sources other than petroleum crude oil for producing the fuel. One such source is what has been termed biological feedstocks. These renewable biological feedstocks include, but are not limited to, plant oils such as corn, jatropha, camelina, rapeseed, canola, soybean and algal oils, animal fats such as tallow, and fish oils. A common feature of these feedstocks is that they are composed of mono- di- and tri-glycerides, and free fatty acids (FAA). The aliphatic carbon chains in the glycerides and FFAs can be saturated or mono-, di- or poly-unsaturated. Most of the glycerides in the renewable feed stocks will be tri-glycerides, but some of the glycerides in the renewable feedstock may be mono-glycerides or di-glycerides. The amount and distribution of compounds such as glycerides may differ between, and be indicative of, biological feedstocks. Biologically-sourced fuel, i.e., fuel that is formulated from the processing of renewable biological feedstock typically retains trace compounds, such as glycerides or FAA, that are not found in petroleum-derived fuels.
Further, all fuels typically retain trace components characteristic of their feed source after processing. Typically, these trace components usually do not affect the bulk fuel properties. For instance, conventional jet fuels may retain trace levels of sulfur and nitrogen heteroatoms characteristic of the oil field or source of the feedstock. Further, these trace components are typically present only in trace levels (i.e., low ppm levels or less) in the processed fuel, and are not easily discernable by standard analytical methods.
While biologically-sourced fuels are generally considered to be more environmentally friendly than petroleum-derived fuels, there are differences in desirability among biologically-sourced fuels depending on the source of the fuel's feedstock. For instance, there may be little demand for biologically-sourced fuels created from plants harvested from protected lands or from ecologically fragile areas or areas of environmental significance. For example, biologically-sourced fuel formulated from palm oil produced as a result of rain forest deforestation is disfavored. Other disfavored biologically-sourced fuels include those formed from food crops, as the use of food crops for fuel causes food price inflation, the diversion of farm land away from food crops to energy crops, or even food shortages. Thus, a potential fuel purchaser may wish to determine the fuel's feedstock before purchase so as to determine if the fuel is from a biologically-sourced feedstock and to discourage production of fuel from undesirable feedstock.
Several biologically-sourced fuels are easily discernable from other fuels, such as petroleum-derived fuels, because they contain compounds having at least one oxygen atom that are present in percent levels in the final blended fuel. Examples include ethanol blended in petroleum-derived gasoline and fatty-acid methyl esters (FAME)—or biodiesel—blended in petroleum-derived diesel. In each of these cases, the ethanol is easily identified from the gasoline in the gasoline blend, and the FAME is easily identified from diesel in the diesel blend.
Other biological-sourced fuels are not easily discernable from petroleum-derived fuels because they are mostly composed of the same components as the petroleum-derived fuel. One example is renewable diesel—or green diesel—a product formed from complete hydrogenation and deoxygenation of biological feedstocks predominantly composed of glycerides and free fatty acids. Green diesel contains mostly paraffins that are not easily distinguished from petroleum-derived paraffins. Another example is Hydrotreated renewable jet fuel (HRJ), also known as green jet fuel, and also known as hydroprocessed esters and free fatty acids (HEFA). This fuel is also produced by complete hydrogenation and deoxygenation of biological feedstocks predominantly composed of glycerides and free fatty acids, but the paraffin product is further processed to produce paraffins in the kerosene range as a drop-in blend for aviation fuel. These biologically-derived paraffins are not easily distinguished from petroleum-derived paraffins.
Accordingly, it is desirable to provide methods for evaluating a fuel to certify that the fuel is biologically-sourced. Further, it is desirable to provide methods for evaluating a fuel to discern a specific feedstock as the source for the fuel. Also, it is desirable to provide methods for evaluating a fuel to determine a characteristic of the fuel based on the identification of trace compounds identified within the fuel when the biological-sourced fuel contains major components indistinguishable from petroleum-derived components. Further, it is desirable to identify these trace compounds when present in only high parts per billion (ppb) to low parts per million (ppm) concentrations. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.